Why should tamoxifen be discontinued prior to surgery?

Tamoxifen Should Be Discontinued Prior to Elective Surgery to Reduce Venous Thromboembolism Risk

Tamoxifen should be considered for discontinuation prior to elective surgery and resumed postoperatively when normal ambulation is restored, primarily to reduce the risk of venous thromboembolism (VTE) during the perioperative period when immobilization compounds the drug's prothrombotic effects. 1, 2, 1

The Core Rationale: Additive VTE Risk

Tamoxifen increases VTE risk through its estrogen-like effects on coagulation factors. The NCCN Breast Cancer Risk Reduction Guidelines consistently recommend considering discontinuation of tamoxifen (or raloxifene) prior to elective surgery across multiple versions 1, 2, 1, 2. This recommendation stems from the recognition that:

• Tamoxifen independently increases VTE risk by approximately 1.9-fold overall, with deep vein thrombosis and pulmonary embolism being the most frequent events 3
• Surgery and immobilization are independent VTE risk factors that create an additive risk when combined with tamoxifen 3
• In the IBIS-I trial, surgery and/or immobilization within 1 month of starting tamoxifen was associated with a 4.7-fold increased risk of VTE (95% CI: 2.2 to 10.1) 3

Practical Implementation

When to Stop

While the NCCN guidelines state to "consider discontinuing" tamoxifen prior to elective surgery 1, the specific timing is not definitively established in these guidelines. However, based on the drug's pharmacokinetics and clinical experience:

• Tamoxifen has a long half-life (approximately 5-7 days for the parent compound)
• Some surgical literature suggests stopping 5 weeks before major surgery to allow adequate clearance 4
• The decision should weigh the type and duration of surgery, expected immobilization period, and individual VTE risk factors

When to Resume

The guidelines are clearer on resumption: restart tamoxifen postoperatively when ambulation is normal 1, 2, 1, 2. This ensures the patient is no longer in the high-risk immobilization period.

Important Caveats and Nuances

The Evidence Is Not Absolute

The NCCN recommendation uses the phrase "consider discontinuing" rather than mandating it 1. This reflects:

• No randomized controlled trials specifically comparing outcomes with versus without perioperative tamoxifen discontinuation
• The recommendation is based on observational data showing increased VTE risk with combined surgery/immobilization and tamoxifen use 3
• Individual risk-benefit assessment is necessary

Contraindications vs. Perioperative Management

It's crucial to distinguish between:

• Absolute contraindications to tamoxifen: history of DVT, PE, stroke, or transient ischemic attack 3, 2 - these patients should not be on tamoxifen at all
• Perioperative discontinuation: a temporary measure in patients already tolerating tamoxifen to reduce additive surgical VTE risk

What About Breast Reconstruction?

Interestingly, recent research challenges the necessity of stopping tamoxifen for microvascular breast reconstruction. A retrospective study found no increased rates of flap thrombosis or failure in patients receiving tamoxifen during TRAM/DIEP flap reconstruction 5. However, another study found increased wound healing complications (61% vs 28%, p<0.001) with perioperative hormone therapy, though not specifically increased thrombotic events 6.

The Oncologic Safety Question

A critical concern is whether stopping tamoxifen perioperatively compromises cancer outcomes. Reassuringly:

• The NSABP B-14 trial showed no "rebound effect" from tamoxifen discontinuation 7
• Brief interruptions for surgery are unlikely to significantly impact long-term efficacy given tamoxifen's long half-life and the years-long treatment duration

Clinical Algorithm

For patients on tamoxifen facing elective surgery:

1. Assess VTE risk factors: age ≥60 years, obesity, prolonged immobilization expected, extensive surgery
2. High-risk surgery (major abdominal, orthopedic, prolonged immobilization): Strongly consider stopping tamoxifen 4-5 weeks preoperatively
3. Moderate-risk surgery: Consider stopping 2-3 weeks preoperatively based on individual factors
4. Minor surgery with minimal immobilization: May continue tamoxifen with appropriate VTE prophylaxis
5. Resume tamoxifen once patient is fully ambulatory, typically 1-2 weeks postoperatively depending on procedure

Common Pitfalls to Avoid

• Don't confuse this with bevacizumab: The guideline evidence about stopping bevacizumab 6 weeks before surgery for wound healing concerns 8 is a different issue than tamoxifen's VTE risk
• Don't stop tamoxifen for thrombotic concerns in patients with prior VTE: These patients shouldn't be on tamoxifen at all 3, 2
• Don't forget to document the plan: Ensure clear communication about when to stop and restart, as patients may be confused about interrupting cancer therapy

The recommendation to hold tamoxifen perioperatively is fundamentally about reducing the compounded VTE risk when the drug's prothrombotic effects meet the high-risk perioperative period, not about wound healing or other surgical complications.